Another Lufthansa Incident
Re the incident report #18; I haven’t managed a translation from the German text so far, but the pictures show the tabs; note ‘glycol’ being mentioned (de-icing fluid). The left picture looks like a servo tab, but the right picture is of the trim tab – dual input rods.
If the tabs froze to the elevator then the elevator should have remained free; the FDR should confirm this. The report of a pitch oscillation also suggests a tab freeze – see #16. If this was the case then some degree of control should have been available via the elevators, assuming that the autopilot was disengaged.
If the initiation of this event was on-ground due to hail, then the blocking the servo tab before takeoff should have been detected during the controls full and free check. Where this is done correctly then both the tab and the elevator should travel full range without any restriction apparent at the control column.
For hail to freeze in the elevator-to-tailplane gap (elevator frozen) then there would have to be a significant amount (volume) of soft hail as the gap size is larger than that of the tab-to-elevator gap.
A rare event involving a known hazard ... providing that all of the holes don't line up in the Swiss Cheese.
If the tabs froze to the elevator then the elevator should have remained free; the FDR should confirm this. The report of a pitch oscillation also suggests a tab freeze – see #16. If this was the case then some degree of control should have been available via the elevators, assuming that the autopilot was disengaged.
If the initiation of this event was on-ground due to hail, then the blocking the servo tab before takeoff should have been detected during the controls full and free check. Where this is done correctly then both the tab and the elevator should travel full range without any restriction apparent at the control column.
For hail to freeze in the elevator-to-tailplane gap (elevator frozen) then there would have to be a significant amount (volume) of soft hail as the gap size is larger than that of the tab-to-elevator gap.
A rare event involving a known hazard ... providing that all of the holes don't line up in the Swiss Cheese.
